1. Field of the invention
This invention relates to radial pneumatic tires used for light to heavy vehicles, and more particular to the design of the lower sidewall and bead area to reduce bead mass and rolling resistance with no substantial effect on load supporting capability.
2. Description of the Art
The continued interest in saving the amount of fuel consumed by vehicles has resulted in a need to reduce vehicle mass. This is true for all components of the vehicle, including the tires. However, vehicles are going faster, supporting heavier loads and cornering at higher speeds than ever before. Hence, as the need to reduce tire mass is stronger, the need to support the same or higher loads with the same size tire remains. The problem is that a reduction in tire mass is known to generally yield a reduction in the ability of the tire to support loads. Another important need is to reduce the rolling resistance of tires. Rolling resistance relates directly to fuel consumption and, generally speaking, rolling resistance decreases as tire mass decreases.
A part of the tire that has increased in mass over the years is the lower sidewall and bead areas. The beads transfer the loads from the tire's contact with a ground surface to the rim of the vehicle. The need of modern vehicles, due to their power and maneuverability, to require normal and lareral loads to be transferred more efficiently by the tire to the rim is known. Increased lower sidewall and bead mass is a result of adding additional components and/or making the classical components larger to support higher loads, and to support them more effectively. One component that has been made larger is the bead filler. Additional components include a large outer filler strip. Historically, this trend toward a higher bead mass is illustrated by U.S. Pat. Nos. 1,918,539; 3,052,275; 4,872,497; and 5,085,260.
U.S. Pat. No. 1,918,539 shows a tire with a very small bead mass resulting from smaller structural components required to resist a reduced tire loading. The bead core has a cross-woven fabric cover surrounding it and an intermediate layer of cord fabric. This was probably adequate for the tire loadings of 1931.
Additional components are shown to be added to the bead in U.S. Pat. No. 3,052,275. The carcass layers were anchored around each bead, an apex filler was added above each bead core and an outer filler strip was also added externally of the carcass plies. The tire of U.S. Pat. No. 3,052,275 improved the resistance to ply separation in the bead consistent with the tire loads of 1962.
Durability of the tire described in U.S. Pat. No. 4,872,497 was improved in the bead area by the addition of a relatively large outer filler strip along with a smaller apex filler. The relative dimensions of the apex filler are related to the height of a flange of the vehicle rim in this 1989 patent.
The heavy duty radial tire of U.S. Pat. No. 5,085,260 discloses a smaller apex filler along with a number of carcass layers turned up around the bead core. The length of carcass turn-up portions and the position of the bead core in relation to the rim flange height is used to obtain bead strength. Accuracy in the placement of end points of each carcass layer is important in the teachings of this 1992 patent.
Further components which were often added to the beads to strengthen them and to improve bead endurance are as disclosed in U.S. Pat. Nos. 4,726,408; 4,779,659; and 5,007,472. Components include additional textile reinforced plies around the bead core, textile reinforced cord layers to support the outer filler strip and multiple layers of outer filler strips. These components can provide a relatively small bead of sufficient strength and durability. However, they result in a bead construction which is very complicated to manufacture ;and their use requires extreme care to insure uniformity of the tires. The need to have a relatively small bead capable of ease of manufacture and with adequate strength and durability remains. The ability to use standard components and manufacturing techniques is essential in having a cost effective product.
Changing the shape and dimensions of standard components in the lower sidewall and bead of a tire can affect their ability to resist higher forces and moments. One component which can be easily modified is the bead filler. A bead filler which has been extended radially into the area of the sidewall in U.S. Pat. Nos. 4,640,329; 4,766,940; and 5,048,584. This extension provides improved transverse and radial load supporting capabilities for the tire.
The motorcycle tire of U.S. Pat. No. 4,640,329 has a hard bead filler with a gradually decreasing thickness extending into the sidewall portions of the tire. This tire is claimed to have an improved transverse stiffness and is resistant to cracks in the tread grooves.
The bead filler of U.S. Pat. No. 4,766,940 extends to a mid-sidewall end position and has a gradually decreasing thickness from the bead core to its end position. An additional layer, including reinforcing cords, closely adheres to the bead filler to improve the steering stability (lateral forces) of the tire. The bead filler of U.S. Pat. No. 5,048,584 also extends radially into the mid-sidewall area of the tire. At least two sets of bead reinforcing layers are added to improve the durability of the bead. An outer filler strip is also used in this tire to partition the reinforcing layers.
Even with these changes the need remains to have a lower sidewall and bead structure which has a reduced mass without compromising the ability to sustain the same vehicle loads and without the necessity of added reinforcing layers or other non-standard tire components. A coexisting need is to obtain lower rolling resistance of the tire. Both of these needs should be achieved while maintaining a manufacturing process with limited changes or added costs.